A thin film battery refers to a battery of which basic component elements are formed as thin films to achieve a thin thickness.
A thin film battery has all component elements such as a cathode, an electrolyte and an anode which are formed into solid states, and is manufactured on a thin substrate through a deposition method such as CVD (chemical vapor deposition) or PVD (physical vapor deposition) to have a thickness of about several microns.
A thin film battery provides various advantages in that the likelihood of an explosion to occur is small due to use of a solid electrolyte such as LiPON, high temperature stability is excellent, self-discharge rate is low, and a service life characteristic is excellent.
Meanwhile, because a thin film battery itself is not large in capacity, a technology of electrically connecting at least two thin film batteries by laminating unit thin film batteries in an effort to increase capacity has been suggested in the art.
Korean Unexamined Patent Publication No. 10-2009-0113106 (dated Oct. 29, 2009) discloses a high capacity thin film battery module of a type in which unit thin film batteries are laminated.
According to the document, a first thin film battery and a second thin film battery are laminated in such a type that the first surface (the current collector forming surface) of the first thin film battery and the second surface (the lower surface of a substrate) of the second thin film battery face each other.
However, in such a type of a thin film battery lamination structure, a thick barrier for preventing penetration of moisture should be formed on the thin film battery positioned uppermost, after lamination, and it is difficult to realize external terminals.